diff --git a/builder.sh b/builder.sh
index 5f59e4f..45c685f 100755
--- a/builder.sh
+++ b/builder.sh
@@ -29,6 +29,7 @@ discard_changes() {
 clean_build() {
     echo "Cleaning build..."
     cd "$SOURCE_PATH" || { echo "Failed to navigate to source directory. Exiting."; exit 1; }
+    hg revert --all --no-backup || { echo "Failed to reverse cahnges in Mozilla repository. Exiting."; exit 1; } 
     ./mach clobber || { echo "Failed to clean build. Exiting."; exit 1; }
 }